I would never think of drinking on a run less than 10 miles. Between 10-20 is dependent on the heat. But over 20 miles, yes, these things are nice. You can't even tell you are wearing it. The one I have fits so well and doesn't bounce or chafe.
I have an old Solomon Skin 10 that I use when I am doing longer, harder efforts out beyond 30km. Under 20 miles, I never worry about it unless it is really hot (then I just take one water bottle).
But if I am doing something over 50km, unsupported, (like the PCT or the Alps) or any kind of true wilderness route that basically takes all day, then yes, I use the pack.